In aqueous tea extracts, substances of varying solubilities are encountered. One fraction of the extracted solids is readily soluble in hot or cold water. The remaining fraction, referred to herein for convenience as tea "tannins", is soluble in hot water but essentially insoluble in cold water. The constituents of this second fraction are not necessarily all tannins in a chemical sense, but they behave as tannins and are customarily and collectively referred to in the art as "tannins".
This tannin fraction of tea offers no significant difficulties in the production of hot beverage. Cold and iced tea drinks containing these raw or native tannins, however, are rendered less desirable by the precipitation and cloudiness resultant from their solubility limitations. In addition, the ease and completeness with which dehydrated tea compositions may be reconstituted in water also suffers from the presence of these raw tannins.
One method of the prior art for overcoming these drawbacks of tea products comprises removing the tannin fraction. The remaining cold-water soluble fraction may be consumed or, for example, concentrated and dried to powder form. Pursuant to such practices, however, the insoluble fraction is discarded, thus leading to a substantial loss of normal, flavorful tea component.
One method for avoiding this loss is set forth in U.S. Pat. No. 3,163,539 of Barch. In accordance with the disclosure of this patent, the normally cold-water insoluble tannin fraction of an aqueous tea extract is separated by chilling the extract until precipitation occurs. The precipitate of tannins is then subjected to oxidation under highly basic condition sufficient to improve its solubility. Thereafter the tannin fraction is acidified to return it to normal pH and may be recombined with the other fraction of the original extract.
Among the problems incident to the foregoing cold-water solubilization of tannin, is a requirement that the tannin fraction need be in a highly basic medium to undergo oxidative solubilization. Substantial amounts of alkali or other base must be added to the medium (which by virtue of its tannin content would ordinarily be acidic) in order for the reaction to proceed satisfactorily. This added alkali is not easily separated from the oxidized tannins and therefore may eventually constitute an impurity of any ultimate tea product. Additionally, the reacidification of the medium often necessary after oxidation may further increase the concentration of foreign ingredients in the final beverage product.